1. Field of the Invention
The present invention relates to a variable discharge pump, such as a variable discharge plunger pump including a plurality of plungers for discharging pressurized working fluid by reciprocating motion thereof. Specifically to a volumetric discharge control system for a variable discharge pump which can vary a volumetric discharge of working fluid from the pump according to a required volumetric flow for hydraulic apparatus.
2. Description of the Prior Disclosure
There have been proposed and developed various plunger pumps with a plurality of plungers to pressurize and discharge working fluid such as oil by reciprocating motion thereof. Recently, to obtain high pump performance, there has been proposed a plunger pump including a plurality of pumping units, each being arranged on the pump shaft in such a manner as to be axially offset from each other. Each pumping unit includes a set of plungers and a set of plunger chambers formed on the outer peripheral wall of the pump casing in such a manner that the longitudinal axis of each plunger chamber is radially arranged relative to the central axis of the pump shaft at essentially regular intervals and each plunger chamber slidably accommodates the associated plunger. Each of the plungers reciprocates by rotational movement of an eccentric cam whose cam surface abuts mating surfaces on each plunger in such a manner that the above mentioned mating surfaces are normally biased to the above mentioned cam surface by means of compression springs.
In such conventional radial plunger pumps, working fluid pressurized by plural pumping units is supplied from plural discharge passages respectively communicated with the pumping units through a confluent passage converging the discharge passages at a discharge outlet communicating with an inlet port of a hydraulic apparatus, for example a hydraulic motor. Therefore, the sum of the volumetric discharges from the plural pumping units is supplied to the hydraulic apparatus. One such conventional plunger pump has been disclosed in Japanese Patent First Publication (Tokkai) Showa 58-15769.
In conventional plunger pumps as described previously, since a volumetric flow discharged from the pump is determined by revolution of the pump shaft, irrespective of the flow required for the hydraulic apparatus, an imbalance occurs between the volumetric flow actually supplied by the pump and the volumetric flow required by the hydraulic apparatus. If a relatively great volumetric flow of working fluid is supplied to hydraulic equipment requiring a relatively small volumetric flow, waste and inefficiency are introduced and equipment may be damaged. Such conventional plunger pumps are uneconomical.